Many centrifugal separators for separating liquids from solids (for instance, mother liquor from salt or other granules) require the interior of the separator basket to be scraped during the separating operation to remove the caked build-up of separated material from the basket interior on a controlled basis. Devices for accomplishing this purpose with machines of the contemporary capacity are well known in the art, one particular example of such an apparatus being that disclosed and claimed in U.S. Pat. No. 3,171,809. Other apparatus for accomplishing hydraulic reciprocation is shown in U.S. patents:
U.S. Pat. No. 384,186 PA1 U.S. Pat. No. 1,028,124 PA1 U.S. Pat. No. 2,751,889 PA1 U.S. Pat. No. 2,921,559 PA1 U.S. Pat. No. 3,016,710 PA1 U.S. Pat. No. 4,037,520 PA1 U.S. Pat. No. 4,173,303
In the apparatus shown in U.S. Pat. No. 3,171,809, an annular plate-like pusher member is mounted in the basket interior upon the end of a piston rod which is driven by a fluid pressure actuated system to reciprocate cyclically while the basket is revolving to drive the pusher member in axially of the separator basket, thus scraping material collected on the basket peripheral wall clear of the open end of the basket during a forward stroke. The piston rod is coaxially mounted within the rotary drive shaft which drives the separator basket in rotation and is coupled to rotate with the shaft so that the pusher and basket do not rotate relative to each other.
The prior art arrangement involves a more complex hydraulic system not suited to the higher pressures, i.e. up to 30,000 p.s.i. or more, dependent on pump pressures available, to be employed in the new, much larger capacity separator contemplated by the present invention, and the present invention is specifically claimed as an improvement over the reciprocatory system disclosed in U.S. Pat. No. 3,171,809 which it is estimated will increase pump efficiency in the neightborhood of sixty-six percent and result in significantly decreased manufacturing and maintenance costs.
One of the prime objects of the invention is to provide a piston assembly of the character described which eliminates formerly required seals and piston rings which were necessarily utilized to prevent pressure loss from one side of the piston to the other. The present system maintains a constant pressure on both sides of the piston, so that close fits and fine bore finishes for pressure sealing are completely unnecessary, and the device can be much more economically and rapidly constructed and assembled.
Another object of the invention is to provide a more compact and mechanically simple construction which has fewer operating parts and avoids the necessity of providing a control sleeve and actuator rod assembly for mechanically accomplishing what is hydraulically accomplished in the present invention.
Another important object of the invention is to provide a system which is one particularly adapted to providing a heavy thrust on a working stroke and compensating on the return stroke when the resistance to movement of the valve and piston assembly is far less. In the present system, a full, uninterrupted hydraulic fluid supply, constant in pressure and volume, is always in communication with the valve and piston assembly.
Another object of the invention is to provide in such a system a very simple means of adjusting the length of stroke.
Still another object of the invention is to provide a system which will operate in any position of orientation and in which the single control element is entirely enclosed within the primary piston, co-axially within the shafting assembly.
Still a further object of the invention is to provide an assembly in which the differential operating face areas of both primary and pilot pistons permit a single fluid pressure inlet with no interruption of flow in a system in which the pilot valve provides an axial bore for exhaust flow from the piston chamber only on the return stroke of the piston. Since there is an exhaust of fluid only on the return stroke, a pump of lesser capacity will accomplish much more in the system.
Still another object of the invention is to provide an easily assembled device in which a sleeve for the pilot piston can be provided within the main piston and held in place by an end retainer which also functions as a pilot stop face and pilot valve cushioning device, as well as having aperatures for exhaust and pressure communicating with the principal thrust area of the primary piston.
Another object of the invention is to provide an assembly in which the rate of primary piston travel can be easily controlled without in any way interfering with the rate of travel of the primary piston on the working portion of its stroke.